The Terminal High-Altitude Area Defence program, or Thaad, that is being deployed is a land-based system made by Lockheed Martin Corp. that uses truck-mounted launchers to intercept missiles. The decision to send it to Guam is the latest US military response to North Korea's heightened rhetoric. Two Navy destroyers were deployed to the western Pacific this week.

Advertisement

"The United States continues to urge the North Korean leadership to cease provocative threats and choose the path of peace by complying with its international obligations," the Pentagon said. "The United States remains vigilant in the face of North Korean provocations and stands ready to defend US territory, our allies, and our national interests."

North Korea presents a "real and clear danger" to the US and allies in the region, Defence Secretary Chuck Hagel said Wednesday. Kim Jong Un's regime possesses a nuclear weapons capacity as well as the capability to deliver missiles, Hagel said in his first policy speech as secretary, delivered at the National Defense University in Washington.

"They've ratcheted up their bellicose, dangerous rhetoric, and some of the actions they've taken over the last few weeks present a real and clear danger and threat to the interests, certainly of our allies" including South Korea and Japan, Mr Hagel said. He said North Korea also has levelled threats "directly at the United States regarding our base in Guam, threatened Hawaii, threatened the West Coast of the United States."

On Wednesday, the North Korean army said it had final approval to launch "merciless" military strikes on the United States, involving the possible use of "cutting-edge" nuclear weapons.

In a statement published by the official KCNA news agency, the general staff of the Korean People's Army said it was formally informing Washington that US threats would be "smashed by . . . cutting-edge smaller, lighter and diversified nuclear strike means".

"The merciless operation of [our] revolutionary armed forces in this regard has been finally examined and ratified."

The US is taking the threat seriously and is engaged in joint exercises with South Korea as well as working with China to ask its help in defusing the situation, Mr Hagel said.

The Thaad interceptors made by Bethesda, Maryland-based Lockheed are a centrepiece of the regional missile defence that the Obama administration plans to deploy in the Middle East against Iran's medium- and long-range ballistic missiles.

The Pentagon bought 42 interceptors and associated components in fiscal 2012 for $US999 million ($955 million), according to the Defense Department budget.

North Korea has previously threatened to attack its southern neighbour and announced it will restart a mothballed plant that can generate plutonium for nuclear weapons. In the latest escalation of tensions on the Korean peninsula, North Korea Wednesday prevented South Korean workers from entering a jointly run industrial park.